1) without strength, impotent, powerless, weakly, disabled
2) unable to be done, impossible
Part of Speech: adjective
Citing in TDNT: 2:284, 186
From G1 (as a negative particle) and G1415; unable, that is, weak (literally or figuratively); passively impossible: - could not do, impossible, impotent, not possible, weak.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root ἀδύνατος; click on the second column to search for that grammatical form of the root ἀδύνατος; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀδύνατος.